A guess : within the two
tabs secure pages, there are references to images, scripts or stylesheets. Those links will be https links, but the third RewriteCond will not match, therefore they *will* be redirected to an insecure URL.

Check the IIRF logfile to see the evidence. if that's the case then you may want to introduce another rule to exempt all images, stylesheets and scripts from the redirect, assuming that they will only be requested from within a page.